Explanation

• Electrostatics deals with electric charges at rest.
• Gauss's law relates the total electric flux through a closed surface to the net charge enclosed within it.
• The law itself is also valid for moving charges in the broader electromagnetic theory, but electrostatics specifically concerns stationary charges.

Last verified on 02-11-2026

Explanation

Unit of length = velocity x time

Unit of length = speed of light x 1 year

Unit of length = distance travelled by light in 1 year = 1 light year

c = 3 x 10^8 m/s

1 year = 365 days = 365 x 24 x 60 x 60 = 31536000 s = 3.15 x 10^7 s (approx 3.156 x 10^7 s)

Distance = c x t

Distance = 3 x 10^8 x 3.15 x 10^7

Distance = 9.45 x 10^15 m

Last verified on 02-11-2026

Explanation

• Coulomb's law describes the electrostatic force between two stationary point charges.
• It applies to both like and unlike charges.
• Like charges repel, while unlike charges attract.

Last verified on 02-11-2026

Explanation

Formula: U = Q^2 / 2C

C = 60 uF = 60 x 10^-6 F

Q = 3 x 10^-8 C

U = (3 x 10^-8)^2 / (2 x 60 x 10^-6)

U = 9 x 10^-16 / 120 x 10^-6

U = 7.5 x 10^-12 J

Last verified on 02-11-2026

Explanation

• Radioactivity is a nuclear process.
• It is generally unaffected by ordinary changes in temperature, pressure, or external radiation.
• It depends mainly on the nature of the radioactive nucleus.

Last verified on 02-11-2026

Explanation

• Electrons are emitted during beta-minus (β⁻) decay.
• Neutrons can be emitted by certain unstable nuclei through neutron emission.
• Helium nuclei are emitted as alpha (α) particles. Each alpha particle contains two protons and two neutrons.
• Isolated protons are not normally emitted in standard natural radioactive decay processes.

Last verified on 02-11-2026

Explanation

• The ground state of a hydrogen atom is the first energy level (n = 1).
• Its minimum excitation energy is 10.2 eV, required to move an electron from the first orbit to the second orbit (n = 2).
• Since one electron volt corresponds to the energy gained by an electron through a potential difference of one volt, the excitation potential is 10.2 V.

Last verified on 02-11-2026

Explanation

• Cathode rays consist of negatively charged particles called electrons.
• Opposite charges attract each other, so negatively charged cathode rays are attracted towards the positively charged plate.
• This deflection proves that cathode rays carry a negative electric charge.

Last verified on 02-11-2026

Explanation

• Copper sulphate pentahydrate contains five molecules of water of crystallization.
• Its crystals are characteristically bright blue due to the presence of hydrated copper(II) ions.
• On heating, it loses its water of crystallization and becomes white anhydrous copper sulphate (CuSO₄).
• Adding water to anhydrous copper sulphate restores its blue color.

Last verified on 02-11-2026

Explanation

• Hydrogenation is an addition reaction in which hydrogen converts benzene into cyclohexane under suitable conditions.
• Benzene commonly undergoes electrophilic substitution reactions in which a hydrogen atom is replaced by an electrophile.
• Halogenation: A hydrogen atom is replaced by chlorine or bromine.
• Nitration: A nitro group (–NO₂) is introduced into the benzene ring.
• Sulphonation: A sulphonic acid group (–SO₃H) is introduced.

Last verified on 02-11-2026